1. Field of the Invention
The present invention relates to a beam transforming element, illumination optical apparatus, exposure apparatus, and exposure method and, more particularly, to an illumination optical apparatus suitably applicable to exposure apparatus used in production of microdevices such as semiconductor elements, image pickup elements, liquid crystal display elements, and thin-film magnetic heads by lithography.
2. Related Background Art
In the typical exposure apparatus of this type, a beam emitted from a light source travels through a fly's eye lens as an optical integrator to form a secondary light source as a substantial surface illuminant consisting of a number of light sources. Beams from the secondary light source (generally, an illumination pupil distribution formed on or near an illumination pupil of the illumination optical apparatus) are limited through an aperture stop disposed near the rear focal plane of the fly's eye lens and then enter a condenser lens.
The beams condensed by the condenser lens superposedly illuminate a mask on which a predetermined pattern is formed. The light passing through the pattern of the mask is focused on a wafer through a projection optical system. In this manner, the mask pattern is projected for exposure (or transcribed) onto the wafer. The pattern formed on the mask is a highly integrated pattern, and, in order to accurately transcribe this microscopic pattern onto the wafer, it is indispensable to obtain a uniform illuminance distribution on the wafer.
For example, Japanese Patent No. 3246615 owned by the same Applicant of the present application discloses the following technology for realizing the illumination condition suitable for faithful transcription of the microscopic pattern in arbitrary directions: the secondary light source is formed in an annular shape on the rear focal plane of the fly's eye lens and the beams passing the secondary light source of the annular shape are set to be in a linearly polarized state with a direction of polarization along the circumferential direction thereof (hereinafter referred to as a “azimuthal polarization state”).